Solar Terrestrial Activity Report

Last major update issued on August 1, 2007 at 02:20 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-23 (last update July 23, 2007)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update July 23, 2007)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update July 23, 2007)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports (last update July 1, 2007)]

Recent activity

The geomagnetic field was quiet on July 31. Solar wind speed ranged between 481 and 596 km/s (average speed was 531 km/s, decreasing 42 km/s from the previous day) under the influence of a high speed stream from CH280. Another high speed stream associated with CH281 arrived near midnight at ACE.

Solar flux measured at 20h UTC on 2.8 GHz was 68.0. The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 5.5). Three hour interval K indices: 11221112 (planetary), 11331111 (Boulder).

The background x-ray flux is below the class A1 level.

At midnight the visible solar disk was spotless. The solar flare activity level was very low. No C class events were recorded during the day.

Coronal mass ejections (CMEs)

July 29-31: No obvious fully or partly Earth directed CMEs were observed.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A new trans equatorial coronal hole (CH281) was in an Earth facing position on July 29-30. A recurrent coronal hole (CH282) in the southern hemisphere will likely rotate into an Earth facing position on August 2-3.

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Processed SOHO/EIT 195 image at 23:12 UTC on July 31. The darkest areas on the solar disk are likely coronal holes.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor to fair. Propagation on long distance northeast-southwest paths is fair.

Monitoring remarks from a location near N58E06: August 1: Several stations from Argentina had fair to good signals during the night while stations from Brazil were mostly absent. Fair to good signals were noted from several North American stations including 590 VOCM, 800 VOWR, 1010 WINS, 1070 CBA, 1130 WBBR and 1510 WWZN.

Forecast

The geomagnetic field is expected to be quiet to active on August 1-2 due to effects from CH281. Quiet conditions could return on August 3-4, then become quiet to active again on August 5-6 due to a high speed stream from CH282.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)



1) Effects from a coronal hole could reach Earth within the next 5 days. When the high speed stream has arrived the color changes to green.
2) Effects from a CME are likely to be observed at Earth within 96 hours.
3) There is a possibility of either M or X class flares within the next 48 hours.

Green: 0-20% probability, Yellow: 20-60% probability, Red: 60-100% probability.

Active solar regions (Recent map)

Compare to the previous day's image.

Data for all numbered solar regions according to the Solar Region Summary provided by NOAA/SEC. Comments are my own, as is the STAR spot count (spots observed at or inside a few hours before midnight) and data for regions not numbered by SEC or where SEC has observed no spots. SEC active region numbers in the table below and in the active region map above are the historic SEC/USAF numbers.

Active region Date numbered SEC
spot
count
STAR
spot
count
Location at midnight Area Classification Comment
10965 2007.07.28 1   S12W15 0010 AXX spotless
S706 2007.07.29     S08W39      
Total spot count: 1 0  
SSN: 11 0  

Monthly solar cycle data

Month Average solar
flux at Earth
International sunspot number Smoothed sunspot number
2000.04 184.2 125.5 120.8
cycle 23 sunspot max.
2000.07 202.3 170.1 119.8
2001.12 235.1 132.2 114.6 (-0.9)
2006.05 80.9 22.3 17.3 (+0.2)
2006.06 76.5 13.9 16.3 (-1.0)
2006.07 75.7 12.2 15.3 (-1.0)
2006.08 79.0 12.9 15.6 (+0.3)
2006.09 77.8 14.4 15.6 (+0.0)
2006.10 74.3 10.4 14.2 (-1.4)
2006.11 86.3 21.5 12.7 (-1.5)
2006.12 84.5 13.6 12.1 (-0.6)
2007.01 83.3 16.9 (11.9 predicted, -0.2)
2007.02 77.7 10.6 (11.3 predicted, -0.6)
2007.03 72.2 4.8 (10.8 predicted, -0.5)
2007.04 72.4 3.7 (10.8 predicted, unchanged)
2007.05 74.4 11.7 (10.6 predicted, -0.2)
2007.06 73.7 12.0 (10.7 predicted, +0.1)
2007.07 71.6 (1) 15.4 (2) (11.0 predicted, +0.3)

1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz.
2) Unofficial, accumulated value based on the Boulder (NOAA/SEC) sunspot number. The official international sunspot number is typically 30-50% lower.

This report has been prepared by Jan Alvestad. It is based partly on my own observations and analysis, and partly on data from some of these solar data sources. All time references are to the UTC day. Comments and suggestions are always welcome.


[DX-Listeners' Club]